With the recent demands for decrease in the weight, cost or the like of a motor vehicle or the like, there has been proposed a composite metal sheet obtainable by laminating metal sheets on one another with plastics. For example, Japanese Patent Laid-Open No. 84879/1976 and No. 84880/1976 disclose a light-weight laminated steel sheet in which a polypropylene sheet is being interposed between metal sheets. However, the polypropylene is poor in adhesion to metal, heat resistance, mechanical strength and dimensional stability. Particularly, the adhesion of polypropylene to metal is considerably lowered at a high temperature.
Japanese Patent Publication No. 15785/1979 discloses a composite metal sheet structure in which a polyamide sheet is being interposed between metal sheets. The polyamide used in this composite metal sheet is insufficient in mechanical characteristics at a low temperature, water resistance and adhesion to metal sheets. Particularly at a high humidity, polyamide is considerably decreased in the strength of adhesion to metal sheets.
It is an object of the present invention to provide a composite metal sheet in which a metal sheet is being securely bonded to a polymer layer.
It is another object of the present invention to provide a composite metal sheet having a high adhesive strength at a high temperature.
It is a further object of the present invention to provide a composite metal sheet in which a polymer layer excellent in mechanical characteristics, heat resistance, chemical stability, dimensional stability and water resistance is being bonded to a metal sheet.